Power supply



March 5, 1957 J. F. BYRD 2,784,321

POWER SUPPLY Filed May 25, 1953 Y,

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fl TTOR NE Y nited States Patent O POWER SUPPLY John F. Byrd, Ashland, N. J., assigner to Radio Corporation of America, a corporation of Deiaware Application May 25, 1953, Serial No. 357,289

Claims. (Cl. 250-214) This invention relates to sound motion picture theater equipment, and particularly to a power supply unit to provide polarizing potentials to the p'hotocells of a plurality of sound reproducers for a plurality of projectors.

The standard system for supplying polarizing voltages for the photocells in sound reproducers is from an alternating current to direct current power supply of the proper voltage. In such systems, a second unit is generally used as a stand-by or auxiliary unit in case of failure of the connected unit. If one unit fails, the other unit is switched into service, which not only interrupts reproduction for a certain` period, but causes click noises during the switching operation.

The present invention is one which eliminates an auxiliary unit as such by providing two power supply units which are permanently connected to the sound reproducers at all times. By a novel circuit arrangement, there will be no interruption of power to the photocells in the event of failure of one of the units, since either unit is capable of supplying the required power. If one unit does fail, this unit may be repaired during the operation of the other and then restored to the system. No switches are required between units, and thus, no noise is created when one unit fails and it is again restored to the line. This is due to the slow warm-up period required for each unit.

The principal object of the invention, therefore, is to facilitate the supplying of power to a plurality of sound reproducers.

Another object of the invent-ion is to provide an improved power supply system for providing polarizing voltages for photocells of a plurality of sound reproducers.

A further object of the invention is to provide an improved circuit between a power supply and a sound reproducer.

Although the novel features which are believed to be characteristic of this invention will be pointed out with particularity in the appended claims, the manner of its organization and the mode of its operation will be better understood by referring to the following description, read in conjunction with the accompanying schematic drawing, forming a part hereof.

Referring now to the drawing, two identical power supply units of any standard type are shown at 5 and 6. These units may supply 250 volts each between their positive and negative terminals. They are connected in parallel over conductors 8 and 9 and resist-ors 11 and 12 to a common terminal point A. in the present system, these resistors have a value of l00,000 ohms each. The negative terminals of the units are connected together and over conductor 14 to ground. Between point A :and ground, there are two standard regulator tubes 16 and 17, the voltage across these tubes being approximately 130 volts. Since this voltage is too high for photocells, a voltage divider made up of sections 20 and 21 is connected between the point A and ground,

section 20 being 120,000 ohms, and section 21 being 220,000 ohms. The divider provides approximately volts at point B. A condenser 22 of 0.1 microfarad is connected between point B and ground to filter out alternating current variations. From point B, conductors 24 and 25 are connected through the primaries of output transformers 27, 28, and 29 to respective photocells 31, 32, and 33. Thus, the polarizing voltage of substantially 85 volts is placed on the anodes of the respective cells.

As mentioned above, the above power supply system has several advantages. Now, if the output of one of the power supply units 5 or 6 becomes open and its output drops to zero volts, the loading of the power supply units remains the same and the voltage at point A lremains the same. If one of the power supply units becomes shorted, the particular resistor 11 and 12 in series with that particular supply unit is in parallel across the point A and ground, but is of relatively high resistance, which merely drops the current slightly in the regulator tubes, but not enough to render them inoperative. Thus, again the voltage at point A remains the same. If either power supply unit develops hum, the series resistors 11 and 12 plus the capacity action of the regulator tubes 16 and 17 form an effective filter, making the ripple at point A unobjectionable and the direct current voltage at this point again remains the same.

From the above description, it is obvious that although the system simulates an auxiliary power supply and uses the same amount of units as if an auxiliary power supply were used, nevertheless, by the use of both units simultaneously in the type of circuit above described, the failure of any one unit in any manner will not cause any interruption in the service. Furthermore, the failed supply unit miay be repaired and restored to the line without introducing any noise in the sound reproducing system.

The remaining portions of the sound reproducing systenis shown include T pads 35, 36, and 37, which are for the purpose of balancing the 50G-ohm audio outputs from the transformers 27, 2S, and 29 caused by variations in phototube sensitivities. The output of the pads has been fed into respective changeover selectors 38, 39, fand 40 and connected to the power amplifier 41 connected to a speaker 42. Although certain values have been given for the resistors, condenser, and output voltages, it is to be understood that other values may be employed, depending upon the load.

I claim:

l. A power supply system comprising a load, a pair of power supply units having substantially the same output voltage between their positive land negative terminals for supplying said load, a pair of resistors, each resistor having one terminal connected to the respective positive terminal of each of said units, means for connecting the other terminals of said resistors together, a voltage divider unit connected between said interconnected terminals of said resistors and said negative terminals `of said power supply units, a voltage regulator connected between said interconnected terminals of said resistors and said negative terminals of said power supply units, and means .for connecting a point on said voltage divider land said negative terminals of said power supply units to said load.

2. A power supply system in accordance with claim 1, in which said point on said voltage ydivider is substantially the midpoint thereof.

3. A power supply system in accordance with claim 2, in which a condenser is connected between said midpoint and the negative lterminals of said units.

4. A polarizing source for a photocell comprising a I pair of power supply units having substantially the same output voltage between their positive and negative terminals, a pair of resistors having one terminal of one connected to one terminal of the other, means forjconnecting the other terminal ot one resistorto che positive terminal of one ofr said units, means for connecting the other terminal of the other resistor to the positive terminal of said other unit, means for connecting the nega tive terminals of said units to ground, a voltage divider connected between the interconnected terminals of said resistors and ground, a connection between a point on said voltage divider and to Ione terminal of said photocell, the other terminal of said photocell being con- 4 nected to ground, and a voltage regulator connected between the interconnected terminals of said resistors and ground.

5. A polarizing source for `a photocell in accordance with claim 4, in which a condenser is connected between said point on said voltage divider land ground.

References Cited in the iile of this patent UNITED STATES PATENTS 465,594 La Roche Dec. 22, 1891 2,336,673 Cooley Dec. 14, 1943 2,432,151 Hammond Dec. 9, 1947 n nl.. 

